Flexible intermediate bulk containers are used for the transport and/or temporary storage of various types of dry, pourable materials, such as cereal grains, chemical compounds, etc. Virtually any dry material in flake, granule, powder, or other similar form may be held by such bulk containers. These containers, also known as bulk bags or by other similar names, are capable of holding quantities of materials weighing from less than a thousand pounds to well over four thousand pounds, depending upon the density of the material, container size, and other factors.
Such containers are generally formed from sheets of synthetic fabric material, such as polypropylene, polyester or other synthetic fabric materials of the chemical family of Nylon (TM) or the like. Any of these materials may be coated in order to reduce porosity. Typically, such bulk bags measure some 35 inches on a side when empty; the depths of the containers are variable according to the amount of material to be carried in any given container, but generally range from three to seven feet in height.
Bulk containers are presently generally constructed of several sheets of material, which construction therefore requires a seam at each edge. Lifting loops of fabric web material are sewn into the four edge seams at or near the top of the bag. As this web material is some two inches in width, the hem into which the web material is sewn must be some two and a half inches wide in order for the web material to fit into the interior of the hem and stitched in place. When this construction technique is used, a great deal of extra material must be used in order to provide for the required wide hems; typically, 42 inch wide material must be used for the fabrication of a bulk bag measuring 35 inches on a side. In addition, the standard four vertical seams allow for the passage of dust or other fine residue for the bulk commodities carried within the bag, resulting in the need for additional cleanup and, with some materials, the release of potentially hazardous substances.
In order to obviate some of the above problems, bulk containers have been constructed from seamless, tubular fabric material. Such material has many advantages over the use of a plurality of flat sheets sewn together, including lower labor costs for assembly and greater strength as well as the obviation of some of the disadvantages noted above. However, it has proven difficult in some cases to attach securely the lifting loop material to bulk bags of tubular construction, due to the lack of multiple thicknesses of fabric material along seams.
Additionally, in order to comply with both domestic and international shipping regulations, such bags must meet certain standards and pass certain tests. One of the tests requires that a fully loaded bag lying on its side, be capable of being lifted to an upright position and clear of the floor by means of only a single lift strap or loop. The synthetic material of which most bulk bags are made is incapable of withstanding such a test without the addition of reinforcement around the upper perimeter. Such reinforcement is normally accomplished by the addition of web material around the upper perimeter, over the outside of the lifting straps or loops. The additional web material obviously increases the cost involved in the production of such bags.
The need arises for an improved construction of such flexible intermediate bulk containers, which construction provides the required upper peripheral reinforcement and, in at least one embodiment, obviates the need for additional web material for perimeter reinforcement. The construction must also allow for the addition of such web reinforcement of the upper perimeter if desired. In the construction of such containers from planar sheets of material, the construction must be compatible with the seam construction, and in the case of seamless tubular material, the construction must provide the required strength without the need for vertical side seams.